diff: add support for --color

* doc/diffutils.texi (diff Options): Add documentation for --color.
Copied from coreutils ls --color.
* src/context.c (pr_unidiff_hunk): Set the color context.
(print_context_header): Likewise.
(pr_context_hunk): Likewise.
* src/diff.h (enum colors_style): New enum to record when to use colors.
(colors_style): New variable to memorize the argument value.
(set_color_context): Add function definition.
* src/diff.c: : Define COLOR_OPTION.
(specify_colors_style): New function.
(longopts): Add --color.
(main): Handle --color argument.
(option_help_msgid): Add usage string for --color.
* src/normal.c (print_normal_hunk): Set the color context.
* src/side.c (print_1sdiff_line): Likewise.
* src/util.c (print_1_line_nl): New function.
(print_1_line): Make it a wrapper of 'print_1_line_nl'.
(colors_enabled): New boolean variable.
(begin_output): Call check_color_output once the output file is
configured.
(output_1_line): Periodically call `process_signals'.
(caught_signals): New sigset_t.
(colors_enabled): New boolean variable.
(interrupt_signal): New sig_atomic_t.
(stop_signal_count): New sig_atomic_t.
(check_color_output): New function.
(install_signal_handlers): Likewise. Copied from coreutils ls.
(process_signals): Likewise.  Copied from coreutils ls.
(set_color_context): New function.
(sighandler): Likewise.  Copied from coreutils ls.
(stophandler): Likewise.  Copied from coreutils ls.

7 files changed, 471 insertions, 58 deletions

diff --git a/doc/diffutils.texi b/doc/diffutils.texi
index 091257f..b2c39da 100644
--- a/doc/diffutils.texi
+++ b/doc/diffutils.texi
@@ -3742,6 +3742,27 @@ Read and write data in binary mode.  @xref{Binary}.
 Use the context output format, showing three lines of context.
 @xref{Context Format}.
 
+@item --color [=@var{when}]
+@cindex color, distinguishing different context
+Specify whether to use color for distinguishing different contexts,
+like header, added or removed lines.  @var{when} may be omitted, or
+one of:
+@itemize @bullet
+@item none
+@vindex none @r{color option}
+Do not use color at all.  This is the default when no --color option
+is specified.
+@item auto
+@vindex auto @r{color option}
+@cindex terminal, using color iff
+Use color only if standard output is a terminal.
+@item always
+@vindex always @r{color option}
+Always use color.
+@end itemize
+Specifying @option{--color} and no @var{when} is equivalent to
+@option{--color=auto}.
+
 @item -C @var{lines}
 @itemx --context@r{[}=@var{lines}@r{]}
 Use the context output format, showing @var{lines} (an integer) lines of
diff --git a/src/context.c b/src/context.c
index e0f21c4..46b5b1f 100644
--- a/src/context.c
+++ b/src/context.c
@@ -80,6 +80,7 @@ print_context_label (char const *mark,
 void
 print_context_header (struct file_data inf[], char const *const *names, bool unidiff)
 {
+  set_color_context (HEADER_CONTEXT);
   if (unidiff)
     {
       print_context_label ("---", &inf[0], names[0], file_label[0]);
@@ -90,6 +91,7 @@ print_context_header (struct file_data inf[], char const *const *names, bool uni
       print_context_label ("***", &inf[0], names[0], file_label[0]);
       print_context_label ("---", &inf[1], names[1], file_label[1]);
     }
+  set_color_context (RESET_CONTEXT);
 }
 
 /* Print an edit script in context format.  */
@@ -205,14 +207,21 @@ pr_context_hunk (struct change *hunk)
   if (function)
     print_context_function (out, function);
 
-  fputs ("\n*** ", out);
+  putc ('\n', out);
+  set_color_context (LINE_NUMBER_CONTEXT);
+  fputs ("*** ", out);
   print_context_number_range (&files[0], first0, last0);
-  fputs (" ****\n", out);
+  fputs (" ****", out);
+  set_color_context (RESET_CONTEXT);
+  putc ('\n', out);
 
   if (changes & OLD)
     {
       struct change *next = hunk;
 
+      if (first0 <= last0)
+        set_color_context (DELETE_CONTEXT);
+
       for (i = first0; i <= last0; i++)
 	{
 	  /* Skip past changes that apply (in file 0)
@@ -225,23 +234,34 @@ pr_context_hunk (struct change *hunk)
 
 	  prefix = " ";
 	  if (next && next->line0 <= i)
-	    /* The change NEXT covers this line.
-	       If lines were inserted here in file 1, this is "changed".
-	       Otherwise it is "deleted".  */
-	    prefix = (next->inserted > 0 ? "!" : "-");
-
-	  print_1_line (prefix, &files[0].linbuf[i]);
+            {
+              /* The change NEXT covers this line.
+                 If lines were inserted here in file 1, this is "changed".
+                 Otherwise it is "deleted".  */
+              prefix = (next->inserted > 0 ? "!" : "-");
+            }
+	  print_1_line_nl (prefix, &files[0].linbuf[i], true);
+          if (i == last0)
+            set_color_context (RESET_CONTEXT);
+          if (files[0].linbuf[i + 1][-1] == '\n')
+            putc ('\n', out);
 	}
     }
 
+  set_color_context (LINE_NUMBER_CONTEXT);
   fputs ("--- ", out);
   print_context_number_range (&files[1], first1, last1);
-  fputs (" ----\n", out);
+  fputs (" ----", out);
+  set_color_context (RESET_CONTEXT);
+  putc ('\n', out);
 
   if (changes & NEW)
     {
       struct change *next = hunk;
 
+      if (first1 <= last1)
+        set_color_context (ADD_CONTEXT);
+
       for (i = first1; i <= last1; i++)
 	{
 	  /* Skip past changes that apply (in file 1)
@@ -254,12 +274,17 @@ pr_context_hunk (struct change *hunk)
 
 	  prefix = " ";
 	  if (next && next->line1 <= i)
-	    /* The change NEXT covers this line.
-	       If lines were deleted here in file 0, this is "changed".
-	       Otherwise it is "inserted".  */
-	    prefix = (next->deleted > 0 ? "!" : "+");
-
-	  print_1_line (prefix, &files[1].linbuf[i]);
+            {
+              /* The change NEXT covers this line.
+                 If lines were deleted here in file 0, this is "changed".
+                 Otherwise it is "inserted".  */
+              prefix = (next->deleted > 0 ? "!" : "+");
+            }
+	  print_1_line_nl (prefix, &files[1].linbuf[i], true);
+          if (i == last1)
+            set_color_context (RESET_CONTEXT);
+          if (files[1].linbuf[i + 1][-1] == '\n')
+            putc ('\n', out);
 	}
     }
 }
@@ -330,11 +355,13 @@ pr_unidiff_hunk (struct change *hunk)
   begin_output ();
   out = outfile;
 
+  set_color_context (LINE_NUMBER_CONTEXT);
   fputs ("@@ -", out);
   print_unidiff_number_range (&files[0], first0, last0);
   fputs (" +", out);
   print_unidiff_number_range (&files[1], first1, last1);
   fputs (" @@", out);
+  set_color_context (RESET_CONTEXT);
 
   if (function)
     print_context_function (out, function);
@@ -363,25 +390,43 @@ pr_unidiff_hunk (struct change *hunk)
 	  /* For each difference, first output the deleted part. */
 
 	  k = next->deleted;
+          if (k)
+            set_color_context (DELETE_CONTEXT);
+
 	  while (k--)
 	    {
 	      char const * const *line = &files[0].linbuf[i++];
 	      putc ('-', out);
 	      if (initial_tab && ! (suppress_blank_empty && **line == '\n'))
 		putc ('\t', out);
-	      print_1_line (NULL, line);
+	      print_1_line_nl (NULL, line, true);
+
+              if (!k)
+                set_color_context (RESET_CONTEXT);
+
+              if (line[1][-1] == '\n')
+                putc ('\n', out);
 	    }
 
 	  /* Then output the inserted part. */
 
 	  k = next->inserted;
-	  while (k--)
+          if (k)
+            set_color_context (ADD_CONTEXT);
+
+          while (k--)
 	    {
 	      char const * const *line = &files[1].linbuf[j++];
 	      putc ('+', out);
 	      if (initial_tab && ! (suppress_blank_empty && **line == '\n'))
 		putc ('\t', out);
-	      print_1_line (NULL, line);
+	      print_1_line_nl (NULL, line, true);
+
+              if (!k)
+                set_color_context (RESET_CONTEXT);
+
+              if (line[1][-1] == '\n')
+                putc ('\n', out);
 	    }
 
 	  /* We're done with this hunk, so on to the next! */
diff --git a/src/diff.c b/src/diff.c
index efd7e47..536f545 100644
--- a/src/diff.c
+++ b/src/diff.c
@@ -70,6 +70,7 @@ static void add_regexp (struct regexp_list *, char const *);
 static void summarize_regexp_list (struct regexp_list *);
 static void specify_style (enum output_style);
 static void specify_value (char const **, char const *, char const *);
+static void specify_colors_style (char const *);
 static void try_help (char const *, char const *) __attribute__((noreturn));
 static void check_stdout (void);
 static void usage (void);
@@ -136,7 +137,9 @@ enum
   UNCHANGED_GROUP_FORMAT_OPTION,
   OLD_GROUP_FORMAT_OPTION,
   NEW_GROUP_FORMAT_OPTION,
-  CHANGED_GROUP_FORMAT_OPTION
+  CHANGED_GROUP_FORMAT_OPTION,
+
+  COLOR_OPTION,
 };
 
 static char const group_format_option[][sizeof "--unchanged-group-format"] =
@@ -159,6 +162,7 @@ static struct option const longopts[] =
   {"binary", 0, 0, BINARY_OPTION},
   {"brief", 0, 0, 'q'},
   {"changed-group-format", 1, 0, CHANGED_GROUP_FORMAT_OPTION},
+  {"color", 2, 0, COLOR_OPTION},
   {"context", 2, 0, 'C'},
   {"ed", 0, 0, 'e'},
   {"exclude", 1, 0, 'x'},
@@ -627,6 +631,10 @@ main (int argc, char **argv)
 	  specify_value (&group_format[c], optarg, group_format_option[c]);
 	  break;
 
+	case COLOR_OPTION:
+	  specify_colors_style (optarg);
+	  break;
+
 	default:
 	  try_help (NULL, NULL);
 	}
@@ -940,6 +948,8 @@ static char const * const option_help_msgid[] = {
   N_("-d, --minimal            try hard to find a smaller set of changes"),
   N_("    --horizon-lines=NUM  keep NUM lines of the common prefix and suffix"),
   N_("    --speed-large-files  assume large files and many scattered small changes"),
+  N_("    --color[=WHEN]       colorize the output; WHEN can be 'never', 'always',"),
+  N_("                           or 'auto' (the default)"),
   "",
   N_("    --help               display this help and exit"),
   N_("-v, --version            output version information and exit"),
@@ -1008,6 +1018,21 @@ specify_style (enum output_style style)
       output_style = style;
     }
 }
+
+/* Set the color mode.  */
+static void
+specify_colors_style (char const *value)
+{
+  if (value == NULL || STREQ (value, "auto"))
+    colors_style = AUTO;
+  else if (STREQ (value, "always"))
+    colors_style = ALWAYS;
+  else if (STREQ (value, "never"))
+    colors_style = NEVER;
+  else
+    try_help ("invalid color '%s'", value);
+}
+
 
 /* Set the last-modified time of *ST to be the current time.  */
 
diff --git a/src/diff.h b/src/diff.h
index 465e4bc..7bf7344 100644
--- a/src/diff.h
+++ b/src/diff.h
@@ -38,6 +38,19 @@ enum changes
   /* Both deletes and inserts: a hunk containing both old and new lines.  */
   CHANGED
 };
+
+/* When colors should be used in the output.  */
+enum colors_style
+{
+  /* Never output colors.  */
+  NEVER,
+
+  /* Output colors if the output is a terminal.  */
+  AUTO,
+
+  /* Always output colors.  */
+  ALWAYS,
+};
 
 /* Variables for command line options */
 
@@ -83,6 +96,9 @@ enum output_style
 
 XTERN enum output_style output_style;
 
+/* Define the current color context used to print a line.  */
+XTERN enum colors_style colors_style;
+
 /* Nonzero if output cannot be generated for identical files.  */
 XTERN bool no_diff_means_no_output;
 
@@ -383,6 +399,7 @@ extern void output_1_line (char const *, char const *, char const *,
 extern void perror_with_name (char const *);
 extern void pfatal_with_name (char const *) __attribute__((noreturn));
 extern void print_1_line (char const *, char const * const *);
+extern void print_1_line_nl (char const *, char const * const *, bool);
 extern void print_message_queue (void);
 extern void print_number_range (char, struct file_data *, lin, lin);
 extern void print_script (struct change *, struct change * (*) (struct change *),
@@ -390,3 +407,14 @@ extern void print_script (struct change *, struct change * (*) (struct change *)
 extern void setup_output (char const *, char const *, bool);
 extern void translate_range (struct file_data const *, lin, lin,
                              long int *, long int *);
+
+enum color_context
+{
+  HEADER_CONTEXT,
+  ADD_CONTEXT,
+  DELETE_CONTEXT,
+  RESET_CONTEXT,
+  LINE_NUMBER_CONTEXT,
+};
+
+extern void set_color_context (enum color_context color_context);
diff --git a/src/normal.c b/src/normal.c
index 721fd1a..e78e8ba 100644
--- a/src/normal.c
+++ b/src/normal.c
@@ -49,21 +49,43 @@ print_normal_hunk (struct change *hunk)
   begin_output ();
 
   /* Print out the line number header for this hunk */
+  set_color_context (LINE_NUMBER_CONTEXT);
   print_number_range (',', &files[0], first0, last0);
   fputc (change_letter[changes], outfile);
   print_number_range (',', &files[1], first1, last1);
+  set_color_context (RESET_CONTEXT);
   fputc ('\n', outfile);
 
   /* Print the lines that the first file has.  */
   if (changes & OLD)
-    for (i = first0; i <= last0; i++)
-      print_1_line ("<", &files[0].linbuf[i]);
+    {
+      if (first0 <= last0)
+        set_color_context (DELETE_CONTEXT);
+      for (i = first0; i <= last0; i++)
+        {
+          print_1_line_nl ("<", &files[0].linbuf[i], true);
+          if (i == last0)
+            set_color_context (RESET_CONTEXT);
+          if (files[0].linbuf[i + 1][-1] == '\n')
+            putc ('\n', outfile);
+        }
+    }
 
   if (changes == CHANGED)
     fputs ("---\n", outfile);
 
   /* Print the lines that the second file has.  */
   if (changes & NEW)
-    for (i = first1; i <= last1; i++)
-      print_1_line (">", &files[1].linbuf[i]);
+    {
+      if (first1 <= last1)
+        set_color_context (ADD_CONTEXT);
+      for (i = first1; i <= last1; i++)
+        {
+          print_1_line_nl (">", &files[1].linbuf[i], true);
+          if (i == last1)
+            set_color_context (RESET_CONTEXT);
+          if (files[1].linbuf[i + 1][-1] == '\n')
+            putc ('\n', outfile);
+        }
+    }
 }
diff --git a/src/side.c b/src/side.c
index 155512c..a0213c4 100644
--- a/src/side.c
+++ b/src/side.c
@@ -206,6 +206,18 @@ print_1sdiff_line (char const *const *left, char sep,
   size_t c2o = sdiff_column2_offset;
   size_t col = 0;
   bool put_newline = false;
+  bool color_to_reset = false;
+
+  if (sep == '<')
+    {
+      set_color_context (DELETE_CONTEXT);
+      color_to_reset = true;
+    }
+  else if (sep == '>')
+    {
+      set_color_context (ADD_CONTEXT);
+      color_to_reset = true;
+    }
 
   if (left)
     {
@@ -233,6 +245,9 @@ print_1sdiff_line (char const *const *left, char sep,
 
   if (put_newline)
     putc ('\n', out);
+
+  if (color_to_reset)
+    set_color_context (RESET_CONTEXT);
 }
 
 /* Print lines common to both files in side-by-side format.  */
diff --git a/src/util.c b/src/util.c
index 2d6d3fc..78b1a2d 100644
--- a/src/util.c
+++ b/src/util.c
@@ -24,6 +24,22 @@
 #include <system-quote.h>
 #include <xalloc.h>
 #include "xvasprintf.h"
+#include <signal.h>
+
+/* Use SA_NOCLDSTOP as a proxy for whether the sigaction machinery is
+   present.  */
+#ifndef SA_NOCLDSTOP
+# define SA_NOCLDSTOP 0
+# define sigprocmask(How, Set, Oset) /* empty */
+# define sigset_t int
+# if ! HAVE_SIGINTERRUPT
+#  define siginterrupt(sig, flag) /* empty */
+# endif
+#endif
+
+#ifndef SA_RESTART
+# define SA_RESTART 0
+#endif
 
 char const pr_program[] = PR_PROGRAM;
 
@@ -143,6 +159,174 @@ print_message_queue (void)
     }
 }
 
+/* The set of signals that are caught.  */
+
+static sigset_t caught_signals;
+
+/* If nonzero, the value of the pending fatal signal.  */
+
+static sig_atomic_t volatile interrupt_signal;
+
+/* A count of the number of pending stop signals that have been received.  */
+
+static sig_atomic_t volatile stop_signal_count;
+
+/* An ordinary signal was received; arrange for the program to exit.  */
+
+static void
+sighandler (int sig)
+{
+  if (! SA_NOCLDSTOP)
+    signal (sig, SIG_IGN);
+  if (! interrupt_signal)
+    interrupt_signal = sig;
+}
+
+/* A SIGTSTP was received; arrange for the program to suspend itself.  */
+
+static void
+stophandler (int sig)
+{
+  if (! SA_NOCLDSTOP)
+    signal (sig, stophandler);
+  if (! interrupt_signal)
+    stop_signal_count++;
+}
+/* Process any pending signals.  If signals are caught, this function
+   should be called periodically.  Ideally there should never be an
+   unbounded amount of time when signals are not being processed.
+   Signal handling can restore the default colors, so callers must
+   immediately change colors after invoking this function.  */
+
+static void
+process_signals (void)
+{
+  while (interrupt_signal || stop_signal_count)
+    {
+      int sig;
+      int stops;
+      sigset_t oldset;
+
+      set_color_context (RESET_CONTEXT);
+      fflush (stdout);
+
+      sigprocmask (SIG_BLOCK, &caught_signals, &oldset);
+
+      /* Reload interrupt_signal and stop_signal_count, in case a new
+         signal was handled before sigprocmask took effect.  */
+      sig = interrupt_signal;
+      stops = stop_signal_count;
+
+      /* SIGTSTP is special, since the application can receive that signal
+         more than once.  In this case, don't set the signal handler to the
+         default.  Instead, just raise the uncatchable SIGSTOP.  */
+      if (stops)
+        {
+          stop_signal_count = stops - 1;
+          sig = SIGSTOP;
+        }
+      else
+        signal (sig, SIG_DFL);
+
+      /* Exit or suspend the program.  */
+      raise (sig);
+      sigprocmask (SIG_SETMASK, &oldset, NULL);
+
+      /* If execution reaches here, then the program has been
+         continued (after being suspended).  */
+    }
+}
+
+static void
+install_signal_handlers (void)
+{
+  /* The signals that are trapped, and the number of such signals.  */
+  static int const sig[] =
+    {
+      /* This one is handled specially.  */
+      SIGTSTP,
+
+      /* The usual suspects.  */
+      SIGALRM, SIGHUP, SIGINT, SIGPIPE, SIGQUIT, SIGTERM,
+#ifdef SIGPOLL
+      SIGPOLL,
+#endif
+#ifdef SIGPROF
+      SIGPROF,
+#endif
+#ifdef SIGVTALRM
+      SIGVTALRM,
+#endif
+#ifdef SIGXCPU
+      SIGXCPU,
+#endif
+#ifdef SIGXFSZ
+      SIGXFSZ,
+#endif
+    };
+  enum { nsigs = sizeof (sig) / sizeof *(sig) };
+
+#if ! SA_NOCLDSTOP
+  bool caught_sig[nsigs];
+#endif
+  {
+    int j;
+#if SA_NOCLDSTOP
+    struct sigaction act;
+
+    sigemptyset (&caught_signals);
+    for (j = 0; j < nsigs; j++)
+      {
+        sigaction (sig[j], NULL, &act);
+        if (act.sa_handler != SIG_IGN)
+          sigaddset (&caught_signals, sig[j]);
+      }
+
+    act.sa_mask = caught_signals;
+    act.sa_flags = SA_RESTART;
+
+    for (j = 0; j < nsigs; j++)
+      if (sigismember (&caught_signals, sig[j]))
+        {
+          act.sa_handler = sig[j] == SIGTSTP ? stophandler : sighandler;
+          sigaction (sig[j], &act, NULL);
+        }
+#else
+    for (j = 0; j < nsigs; j++)
+      {
+        caught_sig[j] = (signal (sig[j], SIG_IGN) != SIG_IGN);
+        if (caught_sig[j])
+          {
+            signal (sig[j], sig[j] == SIGTSTP ? stophandler : sighandler);
+            siginterrupt (sig[j], 0);
+          }
+      }
+#endif
+    }
+}
+
+static char const *current_name0;
+static char const *current_name1;
+static bool currently_recursive;
+static bool colors_enabled;
+
+static void
+check_color_output (bool is_pipe)
+{
+  bool output_is_tty;
+
+  if (! outfile || colors_style == NEVER)
+    return;
+
+  output_is_tty = !is_pipe && isatty (fileno (outfile));
+
+  colors_enabled = (colors_style == ALWAYS
+                    || (colors_style == AUTO && output_is_tty));
+
+  if (output_is_tty)
+    install_signal_handlers ();
+}
+
 /* Call before outputting the results of comparing files NAME0 and NAME1
    to set up OUTFILE, the stdio stream for the output to go to.
 
@@ -150,10 +334,6 @@ print_message_queue (void)
    we fork off a 'pr' and make OUTFILE a pipe to it.
    'pr' then outputs to our stdout.  */
 
-static char const *current_name0;
-static char const *current_name1;
-static bool currently_recursive;
-
 void
 setup_output (char const *name0, char const *name1, bool recursive)
 {
@@ -313,6 +493,7 @@ begin_output (void)
 	    outfile = fdopen (pipes[1], "w");
 	    if (!outfile)
 	      pfatal_with_name ("fdopen");
+	    check_color_output (true);
 	  }
 #else
 	char *command = system_quote_argv (SCI_SYSTEM, (char **) argv);
@@ -320,6 +501,7 @@ begin_output (void)
 	outfile = popen (command, "w");
 	if (!outfile)
 	  pfatal_with_name (command);
+	check_color_output (true);
 	free (command);
 #endif
       }
@@ -330,6 +512,7 @@ begin_output (void)
       /* If -l was not specified, output the diff straight to 'stdout'.  */
 
       outfile = stdout;
+      check_color_output (false);
 
       /* If handling multiple files (because scanning a directory),
 	 print which files the following output is about.  */
@@ -630,6 +813,18 @@ print_script (struct change *script,
 void
 print_1_line (char const *line_flag, char const *const *line)
 {
+  print_1_line_nl (line_flag, line, false);
+}
+
+/* Print the text of a single line LINE,
+   flagging it with the characters in LINE_FLAG (which say whether
+   the line is inserted, deleted, changed, etc.).  LINE_FLAG must not
+   end in a blank, unless it is a single blank.  If SKIP_NL is set, then
+   the final '\n' is not printed.  */
+
+void
+print_1_line_nl (char const *line_flag, char const *const *line, bool skip_nl)
+{
   char const *base = line[0], *limit = line[1]; /* Help the compiler.  */
   FILE *out = outfile; /* Help the compiler some more.  */
   char const *flag_format = 0;
@@ -657,10 +852,13 @@ print_1_line (char const *line_flag, char const *const *line)
       fprintf (out, flag_format_1, line_flag_1);
     }
 
-  output_1_line (base, limit, flag_format, line_flag);
+  output_1_line (base, limit - (skip_nl && limit[-1] == '\n'), flag_format, line_flag);
 
   if ((!line_flag || line_flag[0]) && limit[-1] != '\n')
-    fprintf (out, "\n\\ %s\n", _("No newline at end of file"));
+    {
+      set_color_context (RESET_CONTEXT);
+      fprintf (out, "\n\\ %s\n", _("No newline at end of file"));
+    }
 }
 
 /* Output a line from BASE up to LIMIT.
@@ -672,8 +870,21 @@ void
 output_1_line (char const *base, char const *limit, char const *flag_format,
 	       char const *line_flag)
 {
+  const size_t MAX_CHUNK = 1024;
   if (!expand_tabs)
-    fwrite (base, sizeof (char), limit - base, outfile);
+    {
+      size_t left = limit - base;
+      while (left)
+        {
+          size_t to_write = MIN (left, MAX_CHUNK);
+          size_t written = fwrite (base, sizeof (char), to_write, outfile);
+          if (written < to_write)
+            return;
+          base += written;
+          left -= written;
+          process_signals ();
+        }
+    }
   else
     {
       register FILE *out = outfile;
@@ -681,39 +892,85 @@ output_1_line (char const *base, char const *limit, char const *flag_format,
       register char const *t = base;
       register size_t column = 0;
       size_t tab_size = tabsize;
+      size_t counter_proc_signals = 0;
 
       while (t < limit)
-	switch ((c = *t++))
-	  {
-	  case '\t':
-	    {
-	      size_t spaces = tab_size - column % tab_size;
-	      column += spaces;
-	      do
-		putc (' ', out);
-	      while (--spaces);
-	    }
-	    break;
+        {
+          counter_proc_signals++;
+          if (counter_proc_signals == MAX_CHUNK)
+            {
+              process_signals ();
+              counter_proc_signals = 0;
+            }
+
+          switch ((c = *t++))
+            {
+            case '\t':
+              {
+                size_t spaces = tab_size - column % tab_size;
+                column += spaces;
+                do
+                  putc (' ', out);
+                while (--spaces);
+              }
+              break;
+
+            case '\r':
+              putc (c, out);
+              if (flag_format && t < limit && *t != '\n')
+                fprintf (out, flag_format, line_flag);
+              column = 0;
+              break;
+
+            case '\b':
+              if (column == 0)
+                continue;
+              column--;
+              putc (c, out);
+              break;
+
+            default:
+              column += isprint (c) != 0;
+              putc (c, out);
+              break;
+            }
+        }
+    }
+}
 
-	  case '\r':
-	    putc (c, out);
-	    if (flag_format && t < limit && *t != '\n')
-	      fprintf (out, flag_format, line_flag);
-	    column = 0;
-	    break;
 
-	  case '\b':
-	    if (column == 0)
-	      continue;
-	    column--;
-	    putc (c, out);
-	    break;
+void
+set_color_context (enum color_context color_context)
+{
+  process_signals ();
+  if (colors_enabled)
+    {
+      switch (color_context)
+        {
+        case HEADER_CONTEXT:
+          fputs ("\x1B[1m", outfile);
+          break;
 
-	  default:
-	    column += isprint (c) != 0;
-	    putc (c, out);
-	    break;
-	  }
+        case LINE_NUMBER_CONTEXT:
+          fputs ("\x1B[36m", outfile);
+
+          break;
+
+        case ADD_CONTEXT:
+          fputs ("\x1B[32m", outfile);
+          break;
+
+        case DELETE_CONTEXT:
+          fputs ("\x1B[31m", outfile);
+          break;
+
+        case RESET_CONTEXT:
+          fputs ("\x1b[0m", outfile);
+          break;
+
+        default:
+          abort ();
+        }
     }
 }